Is the cellular telephone, perhaps the most widely used electronic device in the world, causing us harm?

The International Telecommunication Union, the United Nations' agency for information and communication technologies, says the number of mobile-phone subscriptions worldwide has reached 4.6 billion, up from just 600 million at the end of 2009. Far from being just a source of communication, the cellular telephone is increasingly being used by people in developing countries for health services and banking, giving the ubiquitous device the potential to affect global health and economies.

But serious questions remain about possible harmful effects of cell-phone usage. A new study of the effects of cell-phone radiofrequency signal exposure on brain glucose metabolism, a marker of brain activity, provides surprising results but no conclusions. The findings are published in the February 23 Journal of the American Medical Association (JAMA).

The source of the study is also surprising: A group of researchers who usually focus on drug and alcohol abuse. Psychiatrist Nora Volkow, M.D., director of the National Institute on Drug Abuse, explained the connection: "For many years, we've been interested in whether the imaging techniques we use to assess brain function—specifically the magnetic fields used in MRI studies—could actually affect brain function. We know from previous studies that the human brain is sensitive to rapidly changing magnetic fields."

Volkow and her fellow researchers conducted a randomized crossover study of 47 healthy participants who had cell phones placed over both ears for two 50-minute sessions, first with both cell phones off and again with only the right cell phone on, with the sound muted. Positron emission tomography was used to measure brain glucose metabolism during the sessions. The result? Increased brain glucose metabolism in the region of the brain closest to the antenna when the cell phone was on, even though it was not actually in use.

The researchers emphasized that the health consequences of these effects on brain glucose metabolism are unknown, but the results point to a conclusion that cell phone use might be able to affect brain function. There was no impact on whole-brain metabolism in this study, so specific effects may depend on the regions of the brain affected.

What's the next step in this line of study? "We are currently evaluating several possible directions," said Volkow. "Are there any effects from a shorter duration of exposure? What is the nature of the post-exposure recovery? Are there long-lasting effects after chronic repeated cell-phone use five, 10, or 15 years later?"

In an editorial related to the study published in the same issue of JAMA, oncologists Henry Lai, M.D., and Lennart Hardell, M.D., of the University Hospital in Orebro, Sweden, pointed out one possible avenue for further exploration: "An important question is whether glucose metabolism in the brain would be chronically increased from regular use of a wireless phone with higher radiofrequency energy than those used in the current study. Potential acute and chronic health effects need to be clarified."

An abstract of "Cell Phone Radiofrequency Radiation Exposure and Brain Glucose Metabolism" is posted at <http://jama.ama-assn.org/content/305/8/808.abstract?sid=f6eec9e8-5305-483b-b4b9-a639436fc840>; an extract of the related editorial is posted at <http://jama.ama-assn.org/content/305/8/828.extract>.